Protection of the nectar chamber at Astrophytum flowers

HOOCK, H. 1988 . Kakt. and. Sukk. Band: 39 Heft (3) Seite 58-61 Schutz der Nektarkammer bei Astrophytum-Blüten

Protection of the nectar chamber at Astrophytum flowers

The beauty of the Astrophytum flowers is the topic of many authors in the extensive and now more than 150 years old Astrophytum literature. One can understand that almost exclusively the outward appearance is treated, little is known to inside structure and function however. Important references to pollinators, customisation mechanisms and phylogenetic progressions, are found just there, however. These aspects shall be explained at the example of the nectar chamber protection.

The self sterile Astrophytums are dependent on extern pollination. The yellow perianth leaves with her velvet brightness and in addition in Neo-Astrophytum the red flower abyss functions as a show apparatus to attract the pollinators from the remoteness. The flower smell of different varieties of Astrophytum capricorne (Dietrich) Britton & Rose but also this one of Astrophytum myriostigma Lemaire and Astrophytum ornatum (De Candolle) Weber perform an attractive effect. Form and size of the flowers interfere with the visitor circle. While the Astrophytum myriostigma flower as a typical bee flower, bumble-bees and day butterflies with long trunks should be of larger importance at the other species of the genus. One cannot exclude even hummingbirds, although no reliable location observations are known till now. Bird flowers are normally put horizontally at the plants. PORSCH has shown by his studies in 1938 that the flowers of Nopalea cochenillifera (Linne) Salm-Dyck are advertised vertically and visited by hummingbirds of the genus Amazilia mainly. A blue breasted manner, Cyananthus latirostris, is very similar and represented intensively at least at the location of Astrophytum ornatum (SANCHEZ-MEJORADA 1978, own observation in 1986).

Beside the attraction of useful pollinators the flower function has to exclude also unwanted insects. These are ants, small beetles and other insects which search only for nectar without contributing something to the pollination. The length of the flower tube and the area covered by filaments and anthers already forms a first hindrance. A corresponding snout or tongue geometry of the pollinator is required to advance to the nectar chamber. Another mechanism is developed at Astrophytum however, to hold disturbing visitors away: the nectar groove seal.

One finds the nectar groove seal made come true in a different ways, partly in several plant families. LIESS (1983) reports of jamming hair at the local deadly nightshade (Atropa belladonna Linne). A short selection from different cactus genres shall suffice (table 2), as for the rest the literature appendix must be referred for space reasons. Till now, there is no reporting about this unusual flower feature in the genus Astrophytum. Merely KREUZINGER (1935) gives the following note at the Astrophytum from Coahuila: "in few plants there were a cotton wool circle stated in the bottom of the flower tube". HAAGE SADOVSKY (1957) and SADOVSKY SCHÜTZ (1979) repeat this wording without comment. There developed three different types to protect the nectar groove at the Astrophyten clearly. In the simplest case at Astrophytum myriostigma and Astrophytum ornatum the filaments and anthers are pressed thick against the stamp, an access is so aggravated for small insects. Astrophytum asterias (Zuccarini) Lemaire has in addition papilla filaments at the primary group. These are thick hooked in each other and so also fulfil a function in the above meaning. One could also interpret these papillas as sensors for touch attractions but movements of the filaments at Astrophytum asterias are not recognizable.

Tufts of wool hair arise at the Coahuila Astrophytums at the location of the primary filaments. They are lively hooked into another and interwove up between filaments and stamp. The individual threads reach a length up to seven millimetres. They work like a thick felt, to protect the access to the nectar groove. Since the Astrophytum flowers stand vertically, the purpose of this hair cannot consist in preventing the nectar from flowing out. The nectar production is relatively small in the rest. The production seldom suffices to fill up the gutter up to the height of the jamming hair even shortly before the flower closes on the second day of opening. So the task of this "felt" can have to be searched only in connection with the pollinators. This may be a selection for pollinators, which are firm enough to break through the obstacle with her snout or the tongue and hold off the small insects.

The structure of the jamming hair hasn't been different in principle of that one of the shoulder hair in the flower scales. The hair, possibly staminodes, is already free of booth juice in the state of the flower opening. Therefore their cross-cut is flat, they seem drilled and the surface reflection of the light is white. In an individual case hair was found in addition to the seal hair in front of the nectar gutter, between the inner perianth leaves and the first stamen circle. This flower looks from above, as if the jamming hair from below would grow through. Astrophytum asterias, Astrophytum myriostigma and Astrophytum ornatum are free of jamming hair. Single threads in front of the nectar gutter could be proved merely in two of roughly 100 flowers, investigated with a microscope. These were in structure and measurement completely normally and not at all wretched forms. Later seasonally flowers of the same plant were completely free of hair again, however. One could interpret these facts, that the trend for jamming hair formation is characteristically through all Astrophytums but only realized at the Coahuila Astrophytums.

There is a conspicuous and very interesting exception to the described conditions at pure yellow flowering Astrophytum coahuilense and the northern Astrophytum capricorne. Plants of the habitat of the Sierra Anteojo and their naked related existing west of them, are complete or largely free of jamming hair in different cases. It is surprising that the facts in Astrophytum senile var. aureum from the Sierra Paila are rather similar. These plants achieve with their area the southern Sierra La Fragua and the limits of the Bolson of Cuatro Cienegas. The geographical position, the naked epidermis and similar spine morphology as well as the frequent lack of jamming hair in the flower abyss indicate a narrower relationship to Astrophytum capricorne var. niveum (Kayser) Okumura fa. nudum. Perhaps these plants are only another variation of this type, high specified in the spine colour. The recombination of MÖLLER's Echinocactus capricornus var. aureus carried out by BACKEBERG into the Astrophytum senile circle appears from this view as not justified.

Literature:

BACKEBERG,C. (1937): Astrophytum senile var. aureum, Blätter für Kakteenforschung, 1937-2
BEUTELSPACHER, E. R., RAMIREZ, M. M. (1973): Polinicacion en Stenocereus marginatus, Cact. Suc. Mex. 18(3); 80 - 84
BUXBAUM, F. (1950): Morphology of cacti : 89ff, Abbey Garden Press, Pasadena, Section 11
BUXBAUM, F. (1965): Wie untersucht und beschreibt man eine Kakteenblüte? Kakt.and.Sukk. 16 (8) : 146; (9) : 166; (10): 188
HAAGE,W.,SADOVSKY,O. (1957): Kakteen-Sterne : 22, Neumann Verlag Radebeul
HESS,D. (1983): Die Blüte : 149, 150, 283, 287, 309, 311, Verlag Lugen Ulmer Stuttgart
KRAINZ,H. (1956-1975): Die Kakteen, Lieferung 1961 ff, Franckh'sche Verlagshandlung Stuttgart
KREUZINGER, K. (1935): Verzeichnis amerikanischer und anderer Sukkulenten mit Revision der Systematik der Kakteen 20-21, K. Kreuzinger Verlag Eger
MOELLER,H. (1925): Echinocactus capricornus und seine Varietäten, Zeitschrift für Sukkulentenkunde 2 (7): 127129
OCHOTERENA, 1. (1922): Las Cactaceas de Mexico, Puplicadas por la Escuela Nacional Preparatoria: 110-113
PORSCH, 0. (1938): Das Bestäubungsleben der Kakteenblüte 1, Cactaceae; Jahrbücher der Deutschen Kakteen-Gesellschaft eV., Teil 1 :1-80
SADOVSKY,0.,SCHÜTZ,B. (1979): Die Gattung Astrophytum 40, Flora-Verlag Titisee-Neustadt
SANCHEZ-MEJORADA,H. (1978): Manual de Campo de las Cactaceas y Suculentas de la Barranca de Metztitlan, Publicacion de Difusion Cultural 2 : 71
SCHÜTZ, 8. (1973): Astrophytum senile und aureum, Stachelpost 9(44): 41-43
SIMON,W. (1968): Über die Befruchtungsverhältnisse einiger Kakteen: selbststerile Astrophyten, Stachelpost 4 (14) 5-7

photos:

Astrophytum capricorne, Parras, wool-hair in the flower,
Astrophytum asterias
Astrophytum capricorne
Astrophytum capricorne v. niveum f. nudum

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